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l-Phenylalanine, l-tyrosine, and l-DOPA are all precursors to the biological pigment melanin. The enzyme tyrosinase catalyzes the oxidation of l -DOPA to the reactive intermediate dopaquinone , which reacts further, eventually leading to melanin oligomers .
Tyrosine hydroxylase or tyrosine 3-monooxygenase is the enzyme responsible for catalyzing the conversion of the amino acid L-tyrosine to L-3,4-dihydroxyphenylalanine (L-DOPA). [5] [6] It does so using molecular oxygen (O 2), as well as iron (Fe 2+) and tetrahydrobiopterin as cofactors.
Tyrosinase is an oxidase that ... The substrate specificity becomes dramatically restricted in mammalian tyrosinase which uses only L-form of tyrosine or DOPA as ...
In addition to the common amino acid L-tyrosine, which is the para isomer (para-tyr, p-tyr or 4-hydroxyphenylalanine), there are two additional regioisomers, namely meta-tyrosine (also known as 3-hydroxyphenylalanine, L-m-tyrosine, and m-tyr) and ortho-tyrosine (o-tyr or 2-hydroxyphenylalanine), that occur in nature.
According to a review of dopa-responsive dystonias published in 2021, tyrosine hydroxylase deficiency may be hard to diagnose, with a median diagnostic delay of 4 years, [2] and misdiagnosis happens in a significant proportion of patients, with cerebral palsy being the most common erroneous diagnosis.
Dopachrome tautomerase (dopachrome delta-isomerase, tyrosinase-related protein 2), also known as DCT, is a human gene. [5] Its expression is regulated by the microphthalmia-associated transcription factor (MITF).
In the second stage L-DOPA (levodopa) is formed by adding a phenol group to the benzene ring of L-tyrosine. The formation of L-DOPA from L-tyrosine is catalyzed by the enzyme tyrosine hydroxylase. The third stage is the formation of dopamine by removing the carboxylic acid group from L-DOPA, catalysed by the enzyme dopa decarboxylase. [31]
L-DOPA is a tyrosine residue that bears an additional hydroxyl group. The twin hydroxyl groups in each side-chain compete well with water for binding to surfaces, form polar attachments via hydrogen bonds , and chelate the metals in mineral surfaces.